(disclaimer: I work for CodeWeavers, we sell CrossOver which should be a great and easy way to play)
edit: tested out the 20th anniversary update on M2 Pro, it works great!
Better translation layers are what made the Steam Deck possible.
If Apple doesn't care about backwards compatibility on their platform, why should Valve or other developers be burdened with the added cost, especially on a platform with small market share that won't drive many sales?
* I first installed Whisky, a Wine/Game Porting toolkit/app thingy (https://getwhisky.app). Then I installed Steam for Windows inside Whisky, then downloaded HL2. The download was a little bit hiccup-y, but it worked. Testplay of HL2 was great, apart from the mouse.